Investigators discovered a sophisticated cross-border tunnel yesterday extending about a half-mile and found about 2 tons of marijuana on the Mexican end.

The tunnel begins about 85 feet below a small warehouse about 175 yards south of the U.S. border. The other end is in an apparently vacant industrial building in Otay Mesa.

Late last night, authorities were still pulling marijuana out of the tunnel, which is outfitted with electricity and a ventilation system. The building is in an industrial neighborhood near Tijuana’s airport.

“I am deeply concerned,” Hutchison, R-Texas, said in a statement. ”I urge (Department of Homeland Security Secretary Michael) Chertoff to fully investigate this matter and report to Congress the details and confirm whether or not Mexican military officials were involved.”

Also Wednesday, Mexican authorities asked to meet with a West Texas sheriff to view photographs taken during the standoff, which occurred Monday about 50 miles east of El Paso near the Rio Grande international boundary.

Hudspeth County Sheriff Arvin West said the photos show the smugglers’ vehicles as well as scenes of men unloading drugs while fatigue-garbed gunmen stood guard. No shots were fired, he said.

Mexican officials denied the guards were soldiers, asserting they were impostors driving military-style vehicles and wearing uniforms that were not military-issue. Mexican soldiers are prohibited from driving within 3.2 miles of the Texas border, the officials said.

West, however, insisted that the men were Mexican soldiers.

Hutchison linked the incident to larger issues of national security and border protection.

“But make no mistake: This is only a symptom of a much larger problem. Even after 9/11, our nation’s borders remain porous. We must take bold action in securing our borders.”

Armed Mexican government personnel made unauthorized incursions into the United States five times in the last three months of 2005, including one incident last month in Southern California, according to confidential Department of Homeland Security records.

The crossings involved police officers or soldiers in military vehicles and were among 231 such incidents recorded by the U.S. Border Patrol in the last 10 years.

The records obtained by The Times provide new details on more than a dozen incursions into the U.S., including the five most recent ones.

Details of the incidents emerged as authorities on both sides of the border scrambled to investigate a dangerous confrontation Monday in Texas.

Heavily armed personnel in a military-style Humvee from Mexico helped drug smugglers fleeing police to escape back across the border, according to authorities. An internal Border Patrol summary of the incident said the Humvee was equipped with a .50-caliber machine gun.

It was the second such incident in three months in the same rural county southeast of El Paso.

“It’s clear you’re dealing with a large number of incursions by bona-fide Mexican military units, based on the tactics and the equipment being used,” said T.J. Bonner, a Border Patrol veteran and president of the agents union.

U.S. Rep. Tom Tancredo, R-Colo., a frequent critic of the administration’s border security efforts, called Tuesday for the federal government and the governments of southern border states to immediately deploy troops to the U.S.-Mexico border in light of what he termed “recent armed assistance Mexico’s military has given to drug smugglers.”

“Our border has literally turned into a war zone with foreign military personnel challenging our laws and our sovereignty,” Tancredo said.

“The only way to deal with this dangerous situation is to tap the resources of our own military,” Tancredo said. “I call on President Bush and the governors of border states to immediately deploy military personnel to defend our borders against the Mexican military.”

U.S. Sen. Jon Kyl, chairman of the Senate Judiciary Subcommittee on Terrorism and Homeland Security, called on Secretary of State Condoleezza Rice to initiate a formal investigation on the reported border crossings and to begin a dialogue with Mexican officials to prevent further occurrences.

“These illegal incursions are a violation of our sovereignty and pose a significant danger to U.S. law enforcement officials and citizens near the border – especially if all parties involved are armed. The potential for violence is significant.”